docs: def align_after(self, offset):
          """
          Search for a sync point after offset and align just after that.
          """
          f = self.reader
          if offset <= 0:  # FIXME what is a negative offset??
              f.seek(0)
              self._block_count = 0
              self._read_header()  # FIXME we can't extimate how big it is...
              return
          sm = self.sync_marker
          sml = len(sm)
          pos = offset
          while pos < self.file_length - sml:
              f.seek(pos)
              data = f.read(self.FORWARD_WINDOW_SIZE)
              sync_offset = data.find(sm)
              if sync_offset > -1:
                  f.seek(pos + sync_offset)
                  self._block_count = 0
                  return
              pos += len(data)